This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Warm Bodies
In the movie, Perry finding out not only his father but his entire construction crew are zombies.
Though in the book Perry's father dies in a construction accident, the effect is still devastating.
Julie explaining her mother's death to R (in the book).
R seeing Perry's memories from when he died. You could easily tell he was sick and disgusted with himself for what he did. In that scene you can't help but feel sad for him.
R confessing to Julie that he killed Perry in the movie and trying to apologize. Likewise, Julie immediately absorbs it and doesn't appear to blame him. She appears to understand it isn't R's fault that he was trapped by his impulses, but she's still is saddened.